Manufacture of synthetic tanning material free from mineral acid



Patented Mar. 19, 1929.

HTED STATES T706325 PATENT OFFICE.

"JosEr scn irnn, or BASEL, swrrznnnann, ASSIGNOR TO I. n. GEIGY, s. a or 3am,

' SWITZERLAND, A FIRM.

MANUFACTURE OF SYNTHETIC TANNING MATERIAL FREE FROM MINERAL No Drawing. Application filed August 8, 1927, Serial No. 211,680, and in Germany August 16, 1926.

The synthetic tanning materials hitherto known and in commercialuse are organic substances of highly complex molecular structure of strongly acid character, the sol- 5 ubility in water of which relies on the presence of sulpho groups. They are so strongly acid that the hide substance can easily be damaged. Thus it is for example possible to hydrolize completely hides by concentrated solutions of a condensation product from phenolsulphonic acids and formaldehyde. If such synthetic tanning substances are in the form of salts or if the acid products are transformed into their salts, they 1 do not show any useful tanning effect.

Now I have found that such inoperative salts are capable of being restored again to tanning material if they are mixed with salts of hydrofluosilicic acid, which are entirely 2 harmless with respect to the hide substance. One molecule of such a salt corresponds to and replaces herein two molecules of sulphuric acide or soda. If for example the neutralization of a tanning material obtained by condensation of phenolsulphonic acids with formaldehyde needs 106 parts of soda, 94 parts of fluosilicate of sodium or equivalent quantities of another salt of hydrofluosilicic acid are sufiicient to set free again the whole tanning substance, as experiments wit-h hide powder'have proved. Although the described quantities of salts of hydrofiuosilicic acid may be sufiicient to set free the whole of the tanning substance, it may be advantageous in cases where in presence of acid reacting bodies an abundant deposition of tanning matter on the hide fibre is desired, to usean excess of fluosilicates or salts of hydrofiuosilicic acid without injuring the hide substance. There'is then produced silicic acid -which slightly tans the hide, and hydrofluoric acid which transforms the neutralized synthetic tanning material into an active tanning product.

The following examples illustrate the invention, the parts being-by weight:

1. A synthetic tanning'material obtainedfrom cresolsulphonic acid according to known methods is neutralized with soda and dried. 100 parts of the dry product are mixed with 50 parts of fiuosilicate of sodium. The mixture shows contents of tanning matter of 40 to per cent.

The mode of use of such product is as follows: Goat-skin is introduced with 10Q per cent of water into the fulling tub and gradually mixed with 30 per cent (calculated on the skin) of the product obtained according to said Example 1. The tanning operation necessitates 24hours, whereupon'the goods are washed, dried and worked up in the usual manner.

2. A synthetic tanning material obtained according to known methods from a mixture of equal parts of phenolsulphonic and naphtholsulphonic acids is neutralized by means of magnesia and dried. 100 parts of the dryproduct are mixed with 50 parts of fluosilicate of sodium. The mode of use is the same as above.

It may be noted that the'process may be carried out on synthetic tanning matters resulting from any aromatic oxysulphoacids, such as ordinary phenolsulphonic acid, cresolsulphonic acid, naptholsulphonic acid, etc., and formaldehyde, the solubility of which in water relies on the presence of sulpho groups in the molecule.

What I claim is:

' 1. A process for the manufacture of synthetic tanning material free from mineral acid, consisting in mixingsalts of synthetic tanning substances resulting from the condensation of aromatic oxysulphoacids and formaldehyde, the solubility of which in water relies on the presence of sulpho.

groups in the molecule, with salts of hydrofluosilicic acid.

2. A process for the manufacture of synthetic tanning material free from mineral acid, consisting in mixing salts of synthetic tanning substances resultin fromthe condensation of phenolsulphonlc acids and formaldehyde, the solubility of which in water relies on the presence of sulpho groups in the molecule, with salts of hydrofluosilicic acid.

3. As new articles of manufacture, the herein described synthetic tanning materials free from mineral acid, consisting in a mixture of a dr salt of a synthetic tanning substance resu ting from the condensation of aromatic oxysul ho acids and formaldehyde, the solubility 0 which in water relies on the presence of sulpho groups in the molecule, with a salt of hydrofiuosilicic acid.

In witnesswhereof I have hereunto signed my name this 28th day of July, 1927.

' JOSEF SGHAFER. 

